Radiotherapy remains as a major component of treatment modalities for controlling tumor progression and the majority of glioblastoma multiforme (GBM) tumors recur within or at the margin of the radiation field. The unexpected biological effect of irradiation involves an altered profile of MMP-2 and MMP-9 expression and activity and provides evidence of a scenario where irradiation might promote angiogenic and invasion-related gene expression, thereby increasing invasive and angiogenic glioma cell behavior. To elucidate the interactions between radiation and MMPs in glioblastomas, we propose the following specific aims: Specific Aim 1. Determine the effects of irradiation on MMPs/TEMPs in human endothelial and glioblastoma cells, a) Increases in MMP expression and activity during radiation therapy have potential therapeutic implications. We will determine the effects of radiation and glioblastoma-endothelial interactions on MMPs/TIMPs expression, secretion and angiogenesis in vitro in endothelial cells, b) Increased expression and activity of MMPs in irradiated tumor and endothelial cells will be modulated by antagonists and antisense RNAs of MMP-2 and MMP-9 through expression plasmids and adenoviral vectors and will be evaluated in co-cultures for the modulation of angiogenesis in vitro in endothelial cells with and without irradiation. Specific Aim 2. Determine the effects of antisense MMP-2 and MMP-9 inhibition on glioma angiogenesis in vivo. Malignant glioma is one of the most radioresistant tumor types and tumor vascular endothelium is resilient to cytotoxic effects of ionizing radiation. In this aim, we will study the effect of a) adenoviral-mediated antisense suppression of MMP-9 expression under the control of a radiation-responsive (Erg/CMV) chimeric promoter with and without radiation treatment and b) adenoviral-mediated antisense suppression of MMP-9 expression under the control of an endothelial-specific (flt-1) promoter on tumor growth delay, microvessel density, apoptotic index and relative MMPs/TIMPs levels in tumors during tumor growth in the mouse brain. The proposed studies should generate major insights into the pathogenesis of radiation-induced alterations in GBM tumors and, in turn, demonstrate that MMPs inhibition during radiotherapy may represent a new therapeutic approach in improving the therapeutic efficacy of radiotherapy for malignant gliomas.